2.2.2.1. Lines of Evidence

Attribution of observed changes in natural systems to the effects of climate
change is analogous to attribution of anthropogenic greenhouse gases (GHGs)
as causal factors of recent climate trends. Within the climate realm, the lines
of evidence are as follows:

Knowledge of fundamental processes of atmospheric forcing by different
gases and radiative features

General circulation models (GCMs) that accurately "predict" climatic
trends of the 20th century, based on fundamental principles of atmospheric
forcing.

Analyses of global mean temperature and precipitation records that indicate
large variances within and among station data as a result of genuine climate
variance, as well as errors and biases resulting from instrument change, location
changes, or local urbanization. There are large differences in the length
of records because stations have been added over the century. Total record
length may vary widely. This necessitates large-scale analyses that average
the effects over many hundreds or thousands of stations so that the true climate
signal can emerge.

Analogs in the biological realm are as follows:

Knowledge of fundamental responses of organisms to climate and extreme
events. This knowledge is based on experimental work in the laboratory on
physiological thresholds and metabolic costs of different thermal/ water regimes,
as well as experimental work in the field on ecological thresholds and fitness
costs of different temperature/water treatments. In addition to these controlled,
manipulated experiments, there are onsite observations of individuals and
populations before and after particular weather events (e.g., documentation
of population evolution of body size in birds caused by a single winter storm
or a single extreme drought, or population extinctions of butterflies caused
by a single midseason freeze or a single extreme drought year). The biological
community generally accepts the assertion that climate is a major influence
on the abundances and distributions of species.

Geological evidence that shows changes in global mean temperature associated
with changes in the distributions of species. Species' ranges typically
shifted toward the poles by about 400-2,000 km between glacial and interglacial
periods (change of 4°C).

Ecological and biogeographic theory and models that accurately "predict"
current distributions of species, based on fundamental principles of climatic
tolerances.

Analyses of biological records starting from the 1700s, when the first
researchers began to systematically record the timing of biological events
and the locations of species. There are some variances within and among the
historical records for any given species or locality as a result of genuine
variance of the biological trait as well as small errors resulting from changes
in the recorder, methods of recording, local urbanization, and other landscape
changes. There are large differences in the length of records because interest
in taking such records gradually has increased over the centuries. Total record
length may vary from 300 to <10 years. This necessitates large-scale syntheses
that assess the effects over many hundreds of species or studies so that any
true global climate signal can emerge.